On further investigation by the developer , It seems like client sends disconnect message when it is done with remote command execution, ssh-toolkit server is not able to decode this message properly, and kills the session with SIGTERM.
That's why ...
I got a different result here:
lbrito@LW540 ~ $ ssh admin@10.43.2.42 "show version"Keyboard-interactive authentication
Enter password for admin:
Keyboard-interactive authentication
Enter password for admin:
Switch : 800472-00-08 1246G-01386 R...